1. Field of the Invention
The present invention relates to photosensitive and heat-sensitive polymers having sulfonic acid groups and a process for producing the same. More specifically, it relates to photosensitive and heat-sensitive polymers which are sensitive not only to an ultraviolet ray, visible lights and a near infrared ray but also to heat and are useful as an information recording material from the industrial point of view.
2. Description of the Prior Art
As sulfonic acids sensitive to light, aromatic sulfonic acids are well known. For example, as reported in Chemistry and Industry, 21, 399-400 (1977), anthracene-9-sulfonates and naphthalene-1-sulfonates react to a UV ray from a mercury lamp to cause desulfonylation (-SO.sub.2) or desulfonation (-SO.sub.3). Japanese Patent Publication (OPI) No. 118501/1974 discloses a method of forming image patterns by using a CO.sub.2 gas laser beam. This method comprises subjecting the surface layer of a shaped article of an oleophilic resin to chemical treatment to convert the surface layer into a hydrophilic layer and irradiating the hydrophilic layer with a laser beam to selectively remove the hydrophilic layer exposed to the laser beam. As one example of the chemical treatment, compounds having an aromatic ring such as polystyrene are sulfonated. However, in order for the hydrophilic layer to be rendered photosensitive, a UV ray is necessary. Recently, information recording systems using a laser beam which is modulated in response to output signals from a computer have been commercialized, and when the above described materials are employed in these systems, a UV laser beam must be employed. However, the UV laser generator is not only large and expensive but also the sensitivity efficiency is low, and accordingly it is difficult for such a generator to be employed industrially. Further, since the hydrophilic layer is etched by a violent thermal decomposition with the use of a laser beam, a lot of energy is necessary for forming image patterns and the resolution is lowered due to the adhesion of burned scales and polymer scums formed to the imaging portions, and as a result there has been no commercialization of this system.
For example, a compound having a sulfonic acid group in the molecule such as polyvinylsulfonic acid shows neither photosensitivity nor heat-sensitivity. This compound shows characteristic bands near 1050 cm.sup.-1 and near 1175 cm.sup.-1 assignable to sulfonic acid groups in the IR spectrum as illustrated (B) in the drawing (FIGURE). Further, a polymer having aromatic nuclei in the molecule such as polystyrene can easily be sulfonated with concentrated sulfuric acid or fuming sulfuric acid to introduce sulfonic acid groups onto the nuclei but the sulfonated polymer shows neither photosensitivity nor heat-sensitivity. A sulfonated polymer shows a band near 1050 cm.sup.-1 and a characteristic band in the region of 1100 cm.sup.-1 to 1200 cm.sup.-1 assignable to sulfonic acid groups introduced into the aromatic nuclei.
U.S. Pat. No. 3,740,258 discloses resinous enclosure members obtained by sulfonating non-aromatic polymers and describes that with only a trace amount of sulfate, substantially all of the sulfur atoms are present in the form of ##STR1## in the sulfonated polymers. Thus it can be said that these sulfonated polymers substantially show neither photosensitivity nor heat-sensitivity.
Japanese Patent Publication (OPI) No. 52392/1985 discloses planographic printing plate materials obtained by sulfonating the surface of a polymer having a water absorption of at most 0.2%. Such materials require a coating of a photosensitive resin on the surface of the sulfonated polymer for forming image patterns. Further, Japanese Patent Publication (OPI) Nos. 102622/1985 and 132760/1985 disclose a method for preparing offset printing plates by forming a hydrophilic layer on a polymer by various types of treatments including sulfonation and removing the hydrophilic and photosensitive groups by exposure to a flash light with an energy density of at least 3.times.10.sup.2 W/cm.sup.2 for an emission period of time of at most 20 milliseconds or exposure to a laser beam with an energy density of at least 1.times.10.sup.6 W/cm.sup.2. This method which does not require various steps such as developing, fixing, etching and a gum coating process is superior as a method of preparing offset printing plates but disadvantageously requires a light of a high energy density.